Patent Literature 1 or the like proposes a cap having a tamper-resistant function. When such a cap is opened, a connection state between a cap main body and a ring via a coupling portion is released. Once the connection state via the coupling portion is released, a distance between the cap main body and the ring differs from that before the breakage even when the cap main body is attached to an extraction port again. For this reason, one can recognize whether the cap main body has been opened when one looks at it well.